In a silver halide color photographic element or material a color image is formed when the element is given an imagewise exposure to light and then subjected to a color development process. In the color development process silver halide is reduced to silver as a function of exposure by a color developing agent, which is oxidized and then reacts with coupler to form dye. In most color photographic elements the coupler or couplers are coated in the element in the form of small dispersion droplets. Many photographic elements or materials contain, in addition to imaging couplers, image-modifying couplers that release a photographically useful group from the coupling site upon reaction with oxidized color developer. Couplers that release a silver development inhibitor from the coupling-off position, so-called DIR couplers, are one type of image modifying coupler commonly used in color photographic elements to reduce contrast, improve sharpness, reduce granularity and provide color correction.
There are many references to yellow dye-forming couplers in the art. Among them are U.S. Pat. Nos. 3,973,968, 4,022,620 and 5,066,574, which disclose yellow dye-forming couplers with hydantoin-type coupling-off groups. U.S. Pat. Nos. 4,404,727 and 5,451,492 and Canadian Patent 1,039,291 disclose yellow dye-forming couplers with oxazolidinedione coupling-off groups. Yellow couplers with triazole coupling-off groups are disclosed in U.S. Pat. Nos. 3,933,500, 4,182,630 and 5,021,331 and in European Patent 747,763 A1. None of these references discloses the 3-indoloylacetanilide yellow dye-forming couplers of this invention. None of the triazole references discloses yellow couplers with the preferred triazole coupling-off groups of this invention. U.S. Pat. No. 5,674,667 and EPA 751,428 A1 disclose pyrroloylacetanilide yellow dye-forming couplers with a variety of coupling-off groups. The pyrroloylacetanilide couplers of U.S. Pat. No. 5,674,667 are structurally distinct from the 3-indoloylacetanilde couplers of this invention and lack the major advantages of the couplers of this invention.
The yellow dye-forming imaging and image-modifying couplers disclosed in the prior art suffer from a number of deficiencies. Generally, the dyes formed from previously disclosed yellow couplers have low extinction coefficients. This necessitates the coating of more silver and coupler, resulting in increased cost, reduced sharpness (due to additional light scattering) and less rapid processing. In addition, dyes generated from most previously disclosed yellow dye-forming couplers have insufficient thermal or dark stability, leading to undesirable losses in blue density upon long term storage of the photographic materials in which they are utilized. Furthermore, many previously disclosed yellow dye-forming couplers are of low activity, further necessitating additional coupler laydowns.
Thus, a problem to be solved is to provide a photographic element and coupler which exhibit improved color forming ability and improved dye stability.